Abstract
Controller Area Network (CAN) is a fieldbus network suitable for small-scale Distributed Computer Controlled Systems, being appropriate for transferring short real-time messages. However, CAN networks are also known to present some reliability problems, which can lead to an inconsistent message delivery, thus to an unreliable behaviour of the supported applications. In this paper, a set of atomic multicast protocols for CAN networks is presented, preventing the occurrence of such unreliable behaviours. The proposed protocols explore the CAN synchronous properties to minimise its run-time overhead, and to provide a timely service to the supported applications. The paper also presents conclusions drawn from the implementation of the protocols in the Ada version of Real-Time Linux. © Springer-Verlag Berlin Heidelberg 2001.

Abstract
Distributed real time system is a technology that is become widely used in diverse areas of application, including systems in vehicles, aircraft, locomotives, among others. Great part of these applications is considered critic. Hereupon, such systems must be predictable in relation to its logical result and its temporal behavior, same in operating under failure having to provide tolerances. Distributed real time system requires the use of deterministic and reliable communications mechanisms. A high trend in the automotive area is the replacing of great part of the mechanical andlor hydraulic systems for electronic systems, so called control-by-wire. To reach the objectives of the control-by-wire systems, it is necessary the use of distributed real time systems with fault tolerant properties. This work presents a study about the communication requirements in x-by-wire systems. A theoretic content and a detailed study of temporal property of the CAN and TTP/C network communication are presented in the environment of simulation of the x-by-wire system.

Abstract
The WorldFIP protocol is one of the profiles that constitute the European fieldbus standard EN-50170. It is particularly well suited to be used in distributed computer-controlled systems where a set of process variables must be shared among network devices. To cope with the real-time requirements of such systems, the protocol provides communication services based on the exchange of periodic and aperiodic identified variables. The periodic exchanges have the highest priority and are executed at run time according to a cyclic schedule. Therefore, the respective schedulability can be determined at pre-run-time when building the schedule table. Concerning the aperiodic exchanges, the situation is different since their priority is lower and they are handled according to a first-come-first-served policy. In this paper, a, response-time-based schedulability analysis for the real-time traffic is presented. Such analysis considers both types of traffic in an integrated way, according to their priorities. Furthermore, a fixed-priorities-based policy is also used to schedule the periodic traffic. The proposed analysis represents an improvement relative to previous work and it can be evaluated online as part of a traffic online admission control. This feature is of particular importance when a planning scheduler is used, instead of the typical offline static scheduler, to allow online changes to the set of periodic process variables.

Abstract
P-NET is a fieldbus industrial communication standard, which uses a Virtual Token Passing MAC mechanism. In this paper we establish pre-run-time schedulability conditions for supporting real-time traffic with P-NET. Essentially we provide formulae to evaluate the minimum message deadline, ensuring the transmission of real-time messages within a maximum time bound.

Abstract
In this paper, we analyze the ability of the P-NET fieldbus network to cope with the timing requirements of a Distributed Computer Control System (DCCS), where messages associated to discrete events should be made available to a distributed application within a maximum bound time. The major contribution of this paper is the integration of a pre-run-time schedulability analysis of the P-NET protocol with the typical Distributed Computer Controlled System requirements. A case study of a petrochemical DCCS application and its message communication support is presented, stressing some of the timing requirements that must be satisfied by the message exchanges. An implementation supported by a P-NET fieldbus network is then analyzed and some conclusions are drawn about this example.

Abstract